MicroRNAs (miRNAs) comprise a large family of small, ~21?23 nucleotide noncoding RNAs that have emerged as key post-transcriptional regulators of gene expression and act by silencing the translation of target mRNAs. To date, there are ~1,000 predicted human miRNAs believed to control the activity of >60% of all protein-coding genes. Not surprisingly, these small RNAs have been shown to play crucial roles in nearly all aspects of human biology from development to disease. Alteration of miRNA expression, up- or downregulation, has been linked to cancer, obesity, diabetes, viral infections and autoimmune, inflammatory, neurodegenerative and cardiovascular diseases among others. These connections have made the targeting of miRNAs attractive as a novel therapeutic strategy. Our overall goal is to discover and develop selective small molecule inhibitors of miRNA maturation, thus providing the basis for next-generation miR-targeted therapeutics for the treatment of human disease. To do so, we have developed a conceptually new and innovative approach for assaying RNA-small molecule interactions that takes advantage of the power of catalytic signal amplification combined with the selectivity and bioorthogonality of click chemistry. Through this platform assay technology, which we term catalytic assay using enzyme-linked click chemistry assay or cat- ELCCA, we have designed a method that can be implemented in high-throughput, is virtually free of false read- outs and is general for all miRNAs. We propose to further develop and apply cat-ELCCA toward the discovery of pre-miRNA-selective ligands that can be used as chemical probes for targeting miRNAs in disease.